BRUNSWICK, Maine — A quarter of the birds that rely on America’s public lands for habitat are in peril, according to the 2011 State of the Birds report issued by the US Department of the Interior Tuesday.

Nationally, public lands support more than half of the known population of about 300 bird species. And many of the 1,000 species that live in the US — including the 251 that are classified as federally threatened, endangered or of conservation concern — rely on these lands as habitat.

The report finds that America’s public lands and waters, ranging from national wildlife refuges to national parks to national forests, offer “significant opportunities to halt or reverse the decline of many species.”

“The State of the Birds report is a measurable indicator of how well we are fulfilling our shared role as stewards of our nation’s public lands and waters,” Secretary of the Interior Ken Salazar said Tuesday.

Nationally, nearly one-third of U.S. lands and all of our oceans are publicly owned — in 6,000 State Park units, 1,600 Marine Protected Areas, 550 National Wildlife Refuges, 150 National Forests and 394 National Parks.Nature Conservancy staff have worked to secure protection for many of these lands, and frequently work in partnership with state and federal biologists to protect species that use both private and public protected land.

In Maine, where private landowners are an important piece of the solution, providing key habitat on more than 2 million acres of conserved land and millions of additional acres of working forest, public lands have an important role to play, said Nancy Sferra, Director of Science and Stewardship for The Nature Conservancy in Maine.

The Moosehorn National Wildlife Refuge in Washington County, provides important habitat for woodcock, a small migratory forest bird that has declined in recent decades — largely as a result of lost habitat along the Atlantic Flyway, a route that travels through some of the East Coast’s most densely developed areas.

And the Rachel Carson National Wildlife Refuge in Wells protects some of the state’s best piping plover habitat. Between 50 and 75 percent of the plovers, which are federally classified as threatened, and listed by the state as endangered, nest on or near the refuge.

All our coastal waters are publicly owned, and are home to 86 ocean bird species and 173 coastal species. Declining seabird populations indicate severe stress in these ecosystems.

The entire global populations of saltmarsh sparrows are dependent on healthy U.S. coastal marshes, with much of their breeding territory here New England. In addition to the loss of saltmarsh habitat as a result of the combined pressure from coastal development and rising sea levels, studies conducted at Parker River National Wildlife Refuge on Plum Island, off the Massachusetts coast, and at Rachel Carson NWR, suggest that mercury contamination is affecting the ability of the sparrows to successful nest and raise chicks.

“As state and federal leaders increasingly target conservation programs as they seek to balance tight budgets, it’s important to recognize the tremendous conservation value of these protected lands,” Sferra said.

“Although we have made enormous progress in conserving habitat on public lands, we clearly have much more work to do,” Salazar said. “The good news is that because birds so extensively use public lands and waters as habitat, effective management and conservation efforts can make a significant difference in whether these species recover or slide towards extinction.”

The Nature Conservancyis the leading conservation organization working around the world to protect ecologically important lands and waters for nature and people. To date, the Conservancy and its more than one million members have been responsible for the protection of more than 18 million acres in the United States and have helped preserve more than 117 million acres in Latin America, the Caribbean, Asia and the Pacific. Visit The Nature Conservancy on the Web at www.nature.org/maine